1. Field of the Invention
The present invention relates to filters for liquids. More particularly, the present invention is directed to an internal filter for use in the water circulation systems of conventional pools or spas.
2. Description of Related Art
Filters of various configurations are known in the art for use in swimming pools, spas, and the like in order to remove solid particles and debris from the circulated water. Such filters are typically mounted in-line within the pool or spa circulation system and are configured with a liquid-permeable filter media such that, when the circulation system is in operation, the water can be pulled through the filter and pumped back into the pool or spa, leaving the captured debris on the filter for subsequent removal.
The conventional cartridge filter as is known and used in the art is generally comprised of a cylindrical filter element having one or more layers or sheets of a porous material configured with a pore size to allow the passage of water while trapping and removing the solid particles from the water that are unable to pass through the pores. As the filter traps more and more solid particles, the pores in the filter media become clogged, inhibiting the flow of water through the pool or spa's circulation system and thereby decreasing performance and possibly even damaging the circulation pump. In an attempt to address these concerns, the cartridge filters known in the art typically employ relatively large sheets of the porous filter material that are pleated so as to provide an increased filter surface area, thus increasing the life and performance of the filter, while not increasing the filter's overall size. The filter material is maintained in its cylindrical, pleated configuration by being mounted on a rigid cylindrical core and capped on each end by an annular end cap.
Though the conventional cartridge filter is in wide use, there are still several shortcomings with this filter type that have not yet been overcome. First, the flow rate through the cartridge filter is limited by the material and configuration of the pleats and the apertures in the rigid cylindrical core. Such flow rate is typically on the order of 40-70 gpm when the filter is new. Second, despite the overall increased surface area of the filter material achieved by the pleats, only so much of this surface area is truly usable, as the folds of the pleat are tight and are butted up against the cylindrical core. Moreover, as particles and debris become lodged between the pleats, the useful filter surface area that is lost is effectively doubled because the particles and debris clog pores on both adjacent surfaces of the pleat. Thus, cartridge filters become clogged and experience decreased flow rates relatively quickly. A third shortcoming of the cartridge filters known and used in the art is that they cannot be readily cleaned after becoming clogged. In the interest of increasing the total filter surface area, the pleats of the typical cartridge filter are numerous and densely configured about the filter's circumference. Thus, in order to remove the debris trapped deep within the pleat folds, high pressure reverse flow or meticulous debris removal using a vacuum or manual technique between each pleat is necessary. It is further recommended that the cartridge be soaked overnight in a cartridge cleaning solution and then be thoroughly cleaned a second time before being returned to use. Because of these inconveniences, some pool and spa owners simply use their cartridge filters until they become clogged and discard them, often prematurely, rather than bothering to clean them out. Moreover, because cartridge filters trap debris on the outside of the filter only, when the filter is removed from the pool or spa for cleaning or disposal, it is possible that the debris that is loose and easily removed will fall off the filter into the clean side of the circulation system rather than being permanently removed.
For these reasons, other pool and spa filters have been proposed in the art. Diatomaceous earth (“DE”) filters house internal, parallel grids made of extremely fine mesh that is coated with DE, that acts as an adhesive and traps particles and debris from the water as it is filtered through the layers of DE grids. These DE filters are relatively more expensive than comparable cartridge filters and may be subject to municipal or environmental authority regulations pertaining to cleaning and disposal. Similarly, sand filters have also been proposed that essentially use a sand and gravel filter medium that mixes with the circulated water as it passes through the filter to pull out dirt and debris. However, the debris is not permanently captured by the sand filter medium and can eventually work its way through the filter and back into the pool or spa circulation system. It has been proposed that an additional solution be added to the sand to coagulate the particles and debris being filtered into larger clumps that can be more easily trapped by the sand filter medium. As a further maintenance step with sand filters, periodically, the sand itself is depleted from the filter and more sand of a specific type must be added. Sand filters, like the DE filters, are more costly than cartridge filters.
Bag-type filters for separation of unwanted solids from liquid process flows have also been employed in various industrial filtration applications in the interest of increasing flow rate and efficiency. To this end, filter assemblies having bag filters supported on rigid structures or stiffening frames and having elaborate sealing arrangements between the filter and the surrounding housing have been proposed. For example, U.S. Pat. No. 4,769,052 to Kowalski is directed to a flexible fabric filter bag apparatus having multiple support surfaces. A double-walled, porous cylinder cooperates with a stretching frame to suspend and support the filter bag within a rigid cylindrical outer housing. An annular flange is provided in the housing's inner wall and is configured to sealingly engage a metal ring within the bag's open end when the bag, the double-walled cylinder, and the stretching frame are positioned inside the outer housing. A cover is installed over the open end of the outer housing to seal the filter and to force the stretching frame downwardly to draw the filter bag taut against the surfaces of the double-walled support cylinder.
U.S. Pat. No. 5,910,247 to Outterside is directed to a similar filter bag system. Like the Kowalski filter apparatus, Outterside discloses essentially a double-walled filter support cylinder, consisting of an outer basket and an inner tubular member, a housing having a lid for sealing the filter, and a filter bag having a ring in its open end to sealingly engage a flange on the basket. Outterside further discloses specific dimensions for the filter bag which purportedly maximize the surface area without restricting the process flow rate.
Moreover, the Outterside system's supporting structures are configured to prevent collapse of the filter bag when the process flow is reversed to backwash and clean the filter without removing it. Hence, it is essential that the filter bag fit snugly and securely over the outer basket and inner tubular member. To this end, Outterside discloses that the filter body is smaller in diameter than the outside diameter of the tubular support member so that the filter must be stretched to fit over the tubular body and is retained thereon through a frictional fit.
Therefore, the bag filters known and used in the prior art essentially entail a multi-walled support structure that may further include additional stretching or stiffening frames, a filter bag that is secured on the support structure and shaped by the alternative frames, and a filter housing, or vessel, that contains the filter bag assembly and provides for a positive seal between the “dirty” and “clean” side of the filter along a ring integral to the bag's open end. Based on the configuration and number of components in these prior art industrial bag-type filters, it follows that such filters are not well-suited for use in spas because of their complex design and inherent relatively high cost. Furthermore, the housing, which plays a critical role in the function and performance of the prior art bag-type filters, is particularly ill-suited for use in a spa's circulation system because the conventional spa's filter-receiving cavity cannot accommodate the housing, and the housing itself, having only one small inlet strategically positioned above the location where the filter is sealed within the housing, would likely perform poorly under the changing water levels and other conditions of a pool or spa during use.
Thus, there exists a need for an inexpensive, convenient, and functionally efficient filter for use in spas and the like that is both easily reusable and disposable.